Micro perfusion device

ABSTRACT

A micro perfusion device and method for obtaining at least one constituent of a body fluid. The at least one constituent is obtained using a subcutaneously-positioned perfusion catheter into which perfusate is introduced by a supply channel and an injection needle. The perfusate absorbs the at least one constituent as it flows out of the perfusion catheter and through a discharge channel.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a Continuation of U.S. application Ser. No.10/226,104, filed on Aug. 22, 2002 now U.S. Pat. No. 6,706,009, which isa continuation application of International Patent ApplicationPCT/CH01/00095, filed on Feb. 13, 2001, which claims priority to GermanPatent Application No. DE 100 08 825 A1, filed on Feb. 25, 2000, all ofwhich are incorporated by reference herein.

BACKGROUND OF THE INVENTION

The invention relates to a micro perfusion device for obtaining at leastone constituent of a body fluid by means of a subcutaneously positionedperfusion catheter.

FIG. 7D shows a micro perfusion device as described in “Open-FlowMicroperfusion . . . ”, Z. Trajanoski et al., Diabetes Care, Volume 20,Number 7, Jul. 1997, pages 1114 ff. The device comprises a casing 1which may be fixed to the skin. A flexible, permeable perfusion catheter5 a projects from the casing 1, said catheter being subcutaneouslypositioned in a tissue 3. A supply catheter 7 a for a rinsingliquid—referred to as perfusate in the following—protrudes into theperfusion catheter 5 a. The perfusion catheter 5 a and the supplycatheter 7 a form a double-lumen catheter in the tissue 3, comprising aninner lumen within the supply catheter 7 a and a surrounding outer lumenbetween the supply catheter 7 a and the perfusion catheter 5 a. In thecasing 1, the outer lumen feeds into a discharge channel 8 to which adischarge catheter is connected. In order to obtain body fluid from thetissue 3, the perfusate is guided through the supply catheter 7 a upclose to a front distal end of the perfusion catheter 5 a. Once theperfusate has emerged at the front distal of the supply catheter 7 a, itflows back along the supply catheter 7 a in the outer lumen. A rinsingliquid is used as the perfusate which penetrates the constituent whoseconcentration in the body fluid is to be ascertained. Furthermore, bodyfluid is sucked into the outer lumen through the perforated perfusioncatheter 5 a by the rinsing effect. The mixture of perfusate and bodyfluid is discharged through the discharge channel 8 to a measuringmeans. The fluid is conveyed through the device by means of a pump.

The placement procedure prior to the use of the perfusate can be seenfrom FIGS. 7A to 7D. An injection needle 4 a is used to position thedevice. Before it is positioned, the perfusion catheter 5 a tightlysurrounds the injection needle 4 a. Once the skin has been pierced andthe injection needle 4 a positioned in the tissue 3 (FIG. 7A), theinjection needle 4 a is retracted again (FIG. 7B), and the perfusioncatheter 5 a remains in the tissue in the position shown. The supplycatheter 7 a is then inserted through the casing 1 into the perfusioncatheter 5 a (FIG. 7C). It is inserted in the perfusion catheter 5 auntil it takes up most of the length of the perfusion catheter 5 a (FIG.7D). The front end of the supply catheter 7 a is, however, some distanceshort of the front end of the perfusion catheter 5 a.

Micro perfusion devices of the type described require piercing the skin,retracting the injection needle and subsequently providing a perfusatesupply.

BRIEF SUMMARY OF THE INVENTION

It is therefore an object of the invention to provide a micro perfusiondevice which can be easily positioned and operated.

The present invention, in one embodiment, is a micro perfusion devicefor obtaining at least one constituent of a body fluid using asubcutaneously positioned perfusion catheter comprising a casing, asupply for a perfusate, a hollow injection needle, the perfusioncatheter and a discharge channel formed in the casing for dischargingthe perfusate together with the at least one constituent. The injectionneedle comprises a front needle opening, distal when subcutaneouslypositioned, and a rear needle opening. The front needle opening can beformed by a front-facing opening in the conventional way, for example byneedle grinding. It can also be formed by a lateral opening in a surfaceof the injection needle. In one embodiment, the rear needle opening isformed on the rear facing side of the injection needle. It can be formedby a slit or a bore or by laterally cutting the surface area of theinjection needle. The injection needle is accommodated by the casing,and may be slid from a front sliding position to a rear slidingposition. In its front sliding position, it protrudes through theperfusion catheter. In its rear position, it protrudes into theperfusion catheter, however the perfusion catheter protrudes beyond itsfront needle opening in the rear position. The injection needle can be asteel needle. Alternatively, other needles can be used as long as theyhave a sharp tip to cleanly penetrate the skin, are sufficiently rigidfor positioning, and are histocompatible.

The injection needle in one aspect of the invention serves to positionthe perfusion catheter in a tissue whose body fluid and/or from its bodyfluid the at least one constituent is to be obtained. Alternatively, theinjection needle not only fulfills the function of positioning theperfusion catheter, but also fulfills the further function ofintroducing the perfusate into the perfusion catheter. To this end, afluid connection from the perfusate supply into the injection needle isformed by the rear needle opening, at least in the rear sliding positionof the injection needle. When the device is implanted, i.e.subcutaneously positioned, the perfusate is thus introduced through theperfusate supply, the rear needle opening, the hollow injection needleand finally through its front needle opening into the surroundingperfusion catheter and then rinses the perfusion catheter. Since theinjection needle assumes the double function of positioning andintroducing the perfusate, the step of subsequently inserting aperfusate supply into the perfusion catheter can be omitted.

According to one embodiment of the present invention, the microperfusion device can be formed by simply developing catheter heads suchas those for infusing insulin within the framework of diabetotherapy. Aparticularly suitable catheter head is described in DE 198 21 723.4 bythe Applicant. The catheter head described therein already comprises aninjection needle accommodated slidably in the catheter head casing, witha front and a rear needle opening. The rear needle opening is formed bya lateral opening through which, once an infusion catheter has beenpositioned, the insulin solution is supplied for the purpose of primingthe catheter head. With respect to the injection needle of this catheterhead, only a fluid-proof connection is required in the area of the rearneedle opening for supplying the perfusate. Furthermore, a dischargechannel having a fluid-proof connection to the infusion catheter orperfusion catheter, respectively, has to be formed in the catheter head.As a perfusion catheter, the infusion catheter can be perforated.

The micro perfusion device, in one embodiment, serves to measure orascertain the glucose concentration in the body fluid in the vicinity ofthe implanted perfusion catheter. In this case, the at least oneconstituent of the body fluid is glucose. The body fluid together withthe perfusate can be obtained quite simply by the rinsing process. Byusing an appropriate perfusate or rinsing fluid, a particularconstituent can also be selectively obtained by means of the microperfusion device in accordance with the invention, in addition to thebody fluid rinsed with it.

Perfusion, according to one aspect of the present invention, is achievedby suctioning the discharge channel by means of a pump. The perfusatecan also be pressed into the injection needle. Alternatively, it can beconveyed by a combination of pressure and suction.

In one embodiment, the fluid connection between the perfusate supply andthe injection needle only exists in the rear sliding position of theinjection needle. In this case, the perfusate supply is a supply channelformed in the casing. In the rear sliding position, the injection needleopens into this supply channel via its rear needle opening. This ensuresthat the perfusate discharge in the casing is sealed fluid-proof withrespect to the perfusion supply. Appropriate sealing means can beprovided in the casing for this purpose.

In another embodiment, the rear needle opening of the injection needleis permanently connected to the perfusate supply. For this purpose, acatheter forming the perfusate supply can very simply be placed over therear end of the injection needle, which is open-back on its facing side,or otherwise connected fluid-proof to the inner hollow space of theinjection needle.

The perfusion catheter can be formed by a catheter closed on its surfaceside, having only an open front facing side. Alternatively, theperfusion catheter is laterally permeable to the constituent to bemeasured or, selectively, only for the constituent to be measured or forthe body fluid as a whole. The perfusion catheter can be manufacturedfrom a porous material. If the perfusion catheter is perforated, thenthe lateral perforation openings of the perfusion catheter can beelongated in the longitudinal direction of the catheter, in order toobtain as great a stability against straining as possible. Straining thecatheter as it is inserted into the tissue, also known as peal backeffect, is thus prevented or at least kept to a minimum. The perforationopenings can be arranged on gaps or offset with respect to each other,not along a line extending in the longitudinal direction of theperfusion catheter but in the circumferential direction of the perfusioncatheter. The catheter can be perforated as it is formed, orsubsequently, for example using lasers.

In order to obtain a perfusion catheter which is as slim as possible,the outer cross-section of the injection needle and the innercross-section of the perfusion catheter exhibit different shapes, suchthat the perfusion catheter only abuts the injection needle inlongitudinal strips, and a longitudinal gap remains between adjacentlongitudinal strips. In one embodiment, either the injection needle orthe perfusion catheter exhibits a cross-section which deviates from thecircular form. In this form, the perfusion catheter can wrap tightlyaround the injection needle along its entire length situated in thetissue. A flow cross-section for the perfusate flowing back nonethelessremains between the outer surface area of the injection needle and theinner surface area of the perfusion catheter. If, for example, theinjection needle exhibits an outer cross-section deviating from thecircular form along its implanted length, then the perfusion cathetercan exhibit a circular inner cross-section tensed around the needle.Equally, the perfusion catheter can exhibit a non-circular innercross-section and the injection needle a circular outer cross-section.However, it is also possible for the outer cross-section of theinjection needle and the inner cross-section of the perfusion catheterto deviate from the circular form, so long as it is ensured that asufficient flow cross-section for the purpose of rinsing remains betweenthe needle and the perfusion catheter and that the perfusion cathetersurrounds the injection needle, in some embodiments the perfusioncatheter being wrapped tightly around the injection needle, for thepurpose of securely implanting it.

In its rear sliding position, the injection needle is, according to oneaspect of the invention, fixed to the casing in such a way that it canbe tactilely sensed by someone using the micro perfusion device when theinjection needle is in its rear sliding position. The injection needlecan simply be moved into its rear sliding position against a stopper.The injection needle can be fixed not only against sliding further,beyond the rear sliding position, but also against the injection needleadvancing. The injection needle can be fixed to the casing in its rearsliding position by means of a locking connection, such as a detachablelocking connection. For fixing the injection needle, a protrusion, adent, a slit or the like can be formed on the injection needle. In oneembodiment, the rear needle opening is used for the purpose of thelocking connection.

In a further embodiment, the micro perfusion device is not only used toobtain the at least one constituent of the body fluid, butsimultaneously serves as a miniature measuring means or at least as anelectrode platform for a measuring means. The measuring means can serveto measure or ascertain the concentration of the at least oneconstituent in the body fluid. When used as an electrode platform, anelectrode of the measuring means is formed on the lower side of thecasing, via which the casing sits on the tissue. A working electrode ofthe measuring means is electrically connected to the discharged rinsingfluid and can be arranged in the discharge channel of the casing. Theelectrode formed on the lower side of the casing forms the counterelectrode to this working electrode and serves to measure an electricalcurrent and/or an electrical potential. In one aspect of the presentinvention, a sufficiently large bearing area is formed on the lower sideof the casing for the counter electrode to be able to form asufficiently large contact area with the tissue and simultaneously beused as a reference electrode. Furthermore, it can fulfil an adhesivefunction, for adhering to the skin.

When it is formed as a miniature measuring means, a sensor is arrangedin the casing of the micro perfusion device, the sensor in one aspect ofthe invention measuring the concentration of the at least oneconstituent in the body fluid. More precisely, the concentration in theperfusate flowing back is measured and from this, the concentration inthe body fluid are ascertained. The sensor can be arranged in an area ofthe outlet bordering the outer lumen. It can be inserted or recessedinto a side wall of the outlet and, in one embodiment, does not protrudeout of the wall, in order to keep the flow resistance to a minimum.According to another aspect of the invention, no parts of the casingwall or only as much casing wall as is necessary to securely attach thesensor is arranged in the flow path between the outer lumen and thesensor. The sensor is thus arranged as near to the sampling point aspossible, but outside the body.

Although forming it with an integrated sensor, as an electrode platformand as an electrode platform with an integrated sensor are particularlyadvantageous in combination with the micro perfusion device inaccordance with the invention, each of these formations, in particularforming an electrode on the lower side of the casing, can also berealized with all conventional micro perfusion devices.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a cross-sectional view of a micro perfusion device, accordingto one embodiment of the present invention;

FIG. 1B is a cross-sectional view of a portion of a micro perfusiondevice, according to one embodiment of the present invention;

FIG. 2 is a cross-sectional view of a micro perfusion device having nosensors or electrodes, according to one embodiment of the presentinvention;

FIG. 3A is a cross-sectional view of a micro perfusion device before itis positioned in the tissue, according to one embodiment of the presentinvention;

FIG. 3B is a cross-sectional view of a micro perfusion device in itsrear sliding position, according to one embodiment of the presentinvention;

FIG. 4A is a cross-sectional view of an injection needle with anon-circular out cross-section, according to one embodiment of thepresent invention;

FIG. 4B is a cross-sectional view of an injection needle with anon-circular out cross-section, according to one embodiment of thepresent invention;

FIG. 4C is a cross-sectional view of an injection needle with anon-circular out cross-section, according to one embodiment of thepresent invention;

FIG. 5A is a cross-sectional view of a perfusion catheter with anon-circular inner cross-section, according to one embodiment of thepresent invention;

FIG. 5B is a cross-sectional view of a perfusion catheter with anon-circular inner cross-section, according to one embodiment of thepresent invention;

FIG. 5C is a cross-sectional view of a perfusion catheter with anon-circular inner cross-section, according to one embodiment of thepresent invention;

FIG. 6 is a schematic drawing of a micro perfusion system with ameasuring and evaluating means; and

FIG. 7 is a micro perfusion device from the prior art.

DETAILED DESCRIPTION

FIG. 1A shows one embodiment of an implanted micro perfusion device in alongitudinal section. The device comprises a casing 1 with a bearingdisc 2, onto the lower side of which an adhesive patch 15 is attached. Aflexible, perforated perfusion catheter 5 projects perpendicularly fromthe lower side of the bearing disc 2. The perfusion catheter 5concentrically surrounds an injection needle 4 protruding into it. Theinjection needle 4 is formed in the manner of injection needles such asare known from catheter heads for infusing insulin. The injection needle4 is formed by a slim, straight hollow cylinder having a front needleopening 9 at its distal, front facing end and a rear needle opening 10in the surface of the injection needle 4. The injection needle 4 doesnot comprise any other openings. The injection needle 4 encloses aninner lumen L1 between its two openings 9 and 10. An outer lumen L2, inthe form of an annular gap, is formed between the injection needle 4 andthe perfusion catheter 5.

In the casing 1, a discharge channel 8 and a perfusate supply lyingabove it in the form of a supply channel 7 are formed in the bearingdisc. The injection needle 4 is accommodated slidably in the casing,guided in a straight line in the longitudinal direction. The linearguide is formed by a through-bore which projects through the casing 1from an upper side to the opposite lower side. In this way, theinjection needle 4 projects through both the supply channel 7 and thedischarge channel 8. In the supply channel 7, two sealing rings 11 areinserted into two recesses, each encircling the through-bore in theinner wall of the supply channel 7, said sealing rings 11 surroundingthe injection needle 4 in a pressure force seal. In a rear slidingposition of the injection needle 4, shown, the rear needle opening 10comes to rest between the two sealing rings 11. In this way, a fluidconnection between the supply channel 7 and the inner lumen L1 iscreated in the rear sliding position of the injection needle 4, and thesupply channel 7 and discharge channel 8 are constantly separated,fluid-proof.

In the rear sliding position of the injection needle 4, the sealingrings 11 simultaneously establish a locking connection between theinjection needle 4 and the casing 1. In the locking position, i.e. inthe rear sliding position, the two sealing rings 11 are pressed into therear needle opening 10. In this way, a locking or latching effect isachieved. The rear needle opening 10 extends in the longitudinaldirection of the injection needle 4 over such a length that both sealingrings 11 come to rest in the rear needle opening 10 and one each of thetwo sealing rings 11 presses on a rear and a front opening rim,respectively. For providing the locking connection, it would inprinciple be sufficient if only one of the sealing rings 11 came to restbehind the rear or front rim of the rear needle opening 10, in the rearsliding position. However, pressing against both the rear rim andagainst the opposite, front opening rim of the rear needle opening 10creates a locking connection which prevents the injection needle 4 frombeing unintentionally slid in either sliding direction. The fluidconnection between the supply channel 7 and the injection needle 4, aswell as the locking connection between the casing 1 and the injectionneedle 4, are shown again in a separate, enlarged detail in FIG. 1B.

In order to facilitate manually sliding the injection needle 4, theinjection needle 4 is provided with a needle grip 12 on its rear endprotruding out of the casing 1.

FIG. 1A shows one embodiment of the micro perfusion device in itsoperational state during micro perfusion, wherein the injection needle 4is situated in its rear sliding position in the casing 1. Before theperfusion catheter 5 is implanted or positioned in the tissue 3, theinjection needle 4 projects through the perfusion catheter 5 in a frontsliding position. In this initial state, the tip of the injection needle4 including the front needle opening 9 lies beyond the front end of theperfusion catheter 5. In this initial state, the needle grip 12 ispressed up against the surface of the casing 1. In order to position theperfusion catheter 5, the injection needle 4 and the perfusion catheter5, which at least at its front end wraps around the injection needle 4,are pierced through the skin and inserted into the tissue 3, to theposition shown in FIG. 1A. In this position, the bearing disc 2 of thecasing 1 lies flat on the skin via its lower side. The adhesive patch 15attached to the lower side of the bearing disc 2 forms an adhesive areawith the skin. By pressing the casing 1 against the skin, an adhesiveconnection is established. In order to perform micro perfusion, theinjection needle 4 is retracted to the rear sliding position shown inFIG. 1A, once the casing 1 has been positioned and attached. The microperfusion device is then ready for micro perfusion to be performed, inorder to obtain the at least one constituent of the body fluid.

According to one aspect of the invention, the perfusion catheter 5 isperforated with perforation openings 6 in a surface area between itsfront distal end and its rear proximal end bordering the casing 1. Anon-perforated surface area remains in front of the perforated area atthe front end of the perfusion catheter 5. The perfusion catheter 5 isalso non-perforated in the area of its rear end. On its facing side, theperfusion catheter 5 opens forwards. When the perfusion catheter 5 isrinsed, so-called open flow micro perfusion arises. A perfusate isguided through a connected supply catheter into the supply channel 7 ofthe casing 1, enters the hollow injection needle 4 through its rearneedle opening 10, flows through the injection needle 4 and emerges intothe perfusion catheter 5 through the front distal needle opening 9 atthe tip of the needle. Having emerged, the perfusate in the outer lumenL2 between the outer surface of the injection needle 4 and the perfusioncatheter 5 flows back towards the casing 1. As the perfusate flows back,body fluid F is sucked in through the perforation openings 6 due to aresultant jet effect in the outer lumen L2 and carried along in the backflow of perfusate, and selectively, the body fluid constituent to beobtained or a number of body fluid constituents are absorbed through theperforation openings 6 due to a concentration gradient between the bodyfluid F and the perfusate and carried along in the back flow ofperfusate. The perfusate flowing back passes from the outer lumen L2into the discharge channel 8 via a fluid connection formed in the casing1 and then flows through a discharge catheter connected to the dischargechannel 8, into a collecting container. The perfusion catheter 5 isconnected fluid-proof to the casing 1.

In the casing 1, a miniature sensor 13 is arranged in a flowcross-section of the perfusate flowing back. The sensor 13 is arrangedin the discharge channel 8 in the casing 1. In one embodiment, it isarranged immediately downstream of the perfusion catheter 5. The sensor13 need not be implanted but rather can be situated in a flowcross-section outside the tissue 3. In one aspect of the presentinvention, it can be inserted, for example clipped, into the casing 1 atany time, including after the micro perfusion device has beenpositioned.

The micro perfusion device can serve not only as a sensor platform, butcan also serve as an electrode platform for a measuring means. Accordingto one aspect of the invention, a working electrode 14 is formed in thecasing 1 on an inner wall of the discharge channel 8 or forms an area ofthe inner wall. The adhesive patch 15 is itself electrically conductiveand is electrically connected to the skin. It serves the measuring meansas a counter electrode to the working electrode 14. The bearing area ofthe adhesive patch 15 is, in one aspect of the present invention,sufficiently large that it also simultaneously forms a referenceelectrode.

FIG. 2 shows a micro perfusion device according to another embodiment.The device does not have an integrated sensor or integrated electrodes.When using the device, the sensor and the electrodes of the measuringmeans are to be arranged in other known ways.

FIG. 3A and FIG. 3B show an alternative micro perfusion device having aperfusate supply 7 formed by a supply catheter 7 which is directly andpermanently connected to the injection needle 4. Via its rear needleopening 10, the injection needle 4 has a permanent fluid connection tothe supply catheter 7. Thus, the injection needle 4 is linearly guidedin the casing 1 and the perfusate supplied separately from each other.When the injection needle 4 is retracted into its rear sliding position,the supply catheter 7 is moved along with the injection needle 4.

FIG. 3A shows a micro perfusion device in its initial state before it ispositioned in the tissue, the injection needle 4 assuming its frontsliding position with respect to the casing 1 and the perfusion catheter5. The micro perfusion device is also still in this state after it hasbeen positioned in the tissue, until the injection needle 4 is retractedto its rear sliding position. A cut-off valve or slide (not shown) isarranged in a flow cross-section of the supply catheter 7, so that thesupply of perfusate to the injection needle 4 can be interrupted untilperfusion.

FIG. 3B shows the injection needle 4 in its rear sliding position. Byretracting the injection needle 4 some distance behind the front end ofthe perfusion catheter 5, a suitable co-axial flow system is created forthe subsequent perfusion, comprising the lumen L1 enclosed by theinjection needle 4 and the outer lumen L2 formed as an annular spacebetween the injection needle 4 and the perfusion catheter 5. The outerlumen L2 has a fluid connection to the discharge channel 8, again formedin the casing 1, a discharge catheter being connected to said dischargechannel 8. With respect to the other structural features andfunctionality, the embodiments of the first example embodiment apply.

FIGS. 4A-4C and 5A-5C are cross-sections of alternative embodiments ofinjection needles 4 and perfusion catheters 5. The cross-sectionalshapes are adapted such that a sufficient flow cross-section alwaysremains in the outer lumen L2 over the entire flow length of the fluidflowing back, and the perfusion catheter 5 nonetheless tightly surroundsor wraps around the injection needle 4. In FIGS. 4A-4C, the innercross-section of each alternative perfusion catheter 5 is circular inits neutral, untensed state, while the outer cross-section of eachalternative injection needle 4 deviates from the circularcross-sectional shape. In the cross-section combinations in FIGS. 5A-5C,by contrast, the outer cross-section of each alternative injectionneedle 4 is circular, and the inner cross-section of each alternativeperfusion catheter 5 deviates from the circular form.

When installed, the perfusion catheter 5 in one aspect of the inventionis also tensed around the injection needle 4 in its neutral state. Inthis way, partial lumens L2 i through which the perfusate can flow backare formed along and distributed around the injection needle 4, betweenthe points at which the perfusion catheter 5 presses on the injectionneedle 4. By forming the outer cross-section of the injection needle 4and the inner cross-section of the perfusion catheter 5 such that theperfusion catheter 5 only presses on the injection needle 4 inlongitudinal strips and partial lumens 2Li remain between the pressurestrips, the perfusion catheter 5 can be tensed around the injectionneedle 4 over its entire implanted length or at least over a front,partial length. The injection needle 4 thus supports the perfusioncatheter 5, which is advantageous when piercing the skin and insertingit further into the tissue.

FIG. 6 shows a schematic drawing of a perfusion device comprising aconnected measuring and evaluating means. The micro perfusion device isconnected to a supply catheter 7 and a discharge catheter 8. A micropump 16 conveys a perfusate through the supply catheter 7 into theinjection needle 4. The perfusate flowing back is supplied to theexternal sensor 13 and then guided to a collecting container 17 anddisposed of. The perfusate flowing back to the sensor 13 contains the atleast one constituent, whose concentration is to be ascertained bymeasurement. If this constituent is glucose, then the sensor 13 is aglucose sensor. The measuring signals from the sensor 13 are supplied toan evaluation means 18 which ascertains the concentration of the atleast one constituent from them and displays this on a display 19. Inone embodiment, the micro perfusion device is positioned in the tissueof the lower arm. The micro pump 16, the sensor 13, the collectingcontainer 17, a part of the evaluation means 18 and the display 19 canbe collectively accommodated in a lower arm unit. A microprocessor ofthe evaluation means 18 and a battery 20 can be accommodated together ina belt unit and connected to the lower arm unit in order to exchangedata and supply the lower arm unit with power. The evaluation unit 18,in particular the microprocessor, not only evaluates the measuringsignals from the sensor 13 but also controls the micro pump 16.Alternatively, the sensor 13 is not arranged in an external lower armunit but is rather integrated in the casing 1 of the device.

In the foregoing description, embodiments of the invention have beenpresented for the purpose of illustration and description. They are notintended to be exhaustive or to limit the invention to the precise formdisclosed. Obvious modifications or variations are possible in light ofthe above teachings. The embodiments were chosen and described toprovide the best illustration of the principals of the invention and itspractical application, and to enable one of ordinary skill in the art toutilize the invention in various embodiments and with variousmodifications as are suited to the particular use contemplated. All suchmodifications and variations are within the scope of the invention asdetermined by the appended claims when interpreted in accordance withthe breadth they are fairly, legally, and equitably entitled.

Although the present invention has been described with reference topreferred embodiments, persons skilled in the art will recognize thatchanges may be made in form and detail without departing from the spiritand scope of the invention.

1. A micro perfusion device connectable to a perfusate supply and forobtaining at least one constituent of a body fluid, the devicecomprising: a casing including a discharge channel; a perfusion catheterincluding a proximal end in fluid communication with the dischargechannel and a distal end having a distal opening; and a hollow injectionneedle including a proximal end having a proximal opening and a distalend having a discharge opening, wherein said injection needle isslideably displaceable through the casing and the perfusion catheterbetween a forward position and a rearward position, wherein theinjection needle protrudes through the distal opening of the perfusioncatheter when the injection needle is in the forward position, whereinthe discharge opening of the injection needle resides within theperfusion catheter distal when the injection needle is in the rearwardposition, and wherein, in the rearward position, the proximal opening ofthe injection needle is adapted to be in fluid communication with theperfusate supply.
 2. The micro perfusion device of claim 1, wherein theperfusion catheter comprises a catheter surface permeable to the atleast one constituent.
 3. The micro perfusion device of claim 1, whereina cross-sectional shape of the injection needle and a cross-sectionalshape of the perfusion catheter deviate from each other over a lengthalong which the perfusion catheter abuts the injection needle, such thata flow cross-section for the perfusate remains between the injectionneedle and the perfusion catheter.
 4. The micro perfusion device ofclaim 1, wherein the injection needle comprises an outer surface areawhich is not circular when seen in cross-section, over a length alongwhich the perfusion catheter abuts the injection needle.
 5. The microperfusion device of claim 1, wherein the perfusion catheter comprises aninner surface area which is not circular when seen in cross-section,over a length along which the perfusion catheter abuts the injectionneedle.
 6. The micro perfusion device of claim 1, wherein the injectionneedle attaches to the casing in its rearward position.
 7. The microperfusion device of claim 6, wherein the injection needle is attached tothe casing in its rearward position by means of a locking connection. 8.The micro perfusion device of claim 1, wherein the injection needlefurther includes an opening in a proximal surface area of the injectionneedle, wherein the injection needle is slideably locked into therearward position by a sealing ring removeably locked into said opening.9. The micro perfusion device of claim 1, further comprising a supplycatheter connected to an inner lumen enclosed by the injection needle,wherein said supply catheter can be slid together with the injectionneedle relative to the casing, and wherein said supply catheter isadapted to be in fluid communication with the perfusate supply.
 10. Themicro perfusion device of claim 1, wherein a sensor configured tomeasure the concentration of the at least one constituent is disposedwithin the discharge channel.
 11. The micro perfusion device of claim 1,wherein a measuring means for measuring the concentration of the atleast one constituent comprises a working electrode and a counterelectrode, wherein the counter electrode is formed on a lower side ofthe casing, the lower side adapted to contact a tissue surface once thedevice has been positioned.
 12. The micro perfusion device of claim 1,wherein a measuring means for measuring the concentration of the atleast one constituent comprises a working electrode and a counterelectrode, wherein the working electrode is formed in the dischargechannel.
 13. A micro perfusion device connectable to a perfusate supplyand for obtaining at least one constituent of a body fluid, the devicecomprising: a perfusion catheter comprising a distal end including adistal opening and a proximal end in fluid communication with adischarge channel; and a hollow injection needle comprising a distal endincluding a discharge opening and a proximal end including a proximalopening, wherein said injection needle is slideably displaceable throughthe perfusion catheter between an extended position and a retractedposition, wherein the injection needle protrudes through the distalopening of the perfusion catheter when the injection needle is in theextended position, wherein the discharge opening of the injection needleresides within the perfusion catheter when the injection needle is inthe retracted position, wherein the proximal opening of the injectionneedle is adapted to be in fluid communication with the perfusate supplywhen the injection needle is in the retracted position; and wherein,when the injection needle is in the retracted position and perfusate isflowing from the discharge opening of the injection needle, body fluidis sucked into the perfusion catheter.
 14. The micro perfusion device ofclaim 13, further comprising a supply channel connectable to theperfusate supply, wherein the supply channel is adapted to be in fluidcommunication with the proximal end of the injection needle when theinjection needle is in the retracted position, the supply channelcomprising two sealing rings encircling the injection needle, the twosealing rings configured to releasably lock the injection needle intothe retracted position.
 15. The micro perfusion device of claim 14,wherein the injection needle further comprises an opening in the surfaceof the proximal end of the injection needle, wherein the two sealingrings releasably lock the injection needle into the retracted positionby being partially disposed within said opening in the surface of theproximal end of the injection needle when the injection needle is in theretracted position.
 16. The micro perfusion device of claim 13, furthercomprising a sensor configured to provide information regarding the atleast one constituent of the body fluid.
 17. The micro perfusion deviceof claim 16, wherein the sensor is disposed within the dischargechannel.
 18. The micro perfusion device of claim 16, wherein the sensoris external to the device.
 19. The micro perfusion device of claim 18,further comprising: a supply channel in fluid communication with theproximal end of the injection needle; a supply catheter in fluidcommunication with the supply channel and configured to be placed influid communication with the perfusate supply; an external micro pumpadapted to force the perfusate through the supply catheter and thesupply channel and into the injection needle; a discharge catheterfluidly connected to the discharge channel and configured to transportthe perfusate to the sensor; a collecting container configured tocollect the perfusate for disposal; and an evaluation componentelectronically connected to the sensor, the evaluation componentconfigured to ascertain information regarding the at least oneconstituent and display the information on a display.
 20. The microperfusion device of claim 19, further comprising: a microprocessor forthe evaluation component, the microprocessor adapted for locationseparate from the micro perfusion device; and a battery configured toprovide power to the device, the battery also located for locationseparate from the micro perfusion device.
 21. The micro perfusion deviceof claim 13, further comprising a working electrode configured toprovide information regarding the at least one constituent of the bodyfluid.
 22. The micro perfusion device of claim 21, further comprising acasing and a working electrode, wherein the hollow injection needle isslideably displaceable through the casing, wherein the casing isconnected to the proximal end of the perfusion catheter, wherein theworking electrode is located within the casing on an inner wall of thedischarge channel, and wherein an adhesive patch on a lower side of thecasing is configured to serve as a counter electrode to the workingelectrode.
 23. The micro perfusion device of claim 13, wherein theinjection needle is configured to provide support to the perfusioncatheter.
 24. The micro perfusion device of claim 23, wherein theinjection needle and the perfusion catheter are in contact for a fulllength of the injection needle within the perfusion catheter, theinjection needle and the perfusion catheter providing a flow pathconfigured to allow fluid passage.
 25. A method of obtaining at leastone constituent of a body fluid, comprising: providing a perfusioncatheter comprising a proximal end in fluid communication with adischarge channel and a distal end including a distal opening; providinga hollow injection needle slideably displaceable in the perfusioncatheter and including a proximal end capable of being placed in fluidcommunication with a perfusate and a distal end including a dischargeopening; extending the distal end of the injection needle through thedistal opening of the perfusion catheter; and inserting the perfusioncatheter into a tissue containing the at least one constituent when thedistal end of the injection needle is protruding from the distal end ofthe perfusion catheter.
 26. The method of claim 25, further comprisingretracting the injection needle until the discharge opening of theinjection needle is within the perfusion catheter.
 27. The method ofclaim 26, wherein retracting the injection needle positions the proximalopening in fluid communication with the perfusate.
 28. The method ofclaim 26, further comprising causing perfusate to flow through theinjection needle, out the discharge opening of the injection needle, andinto the perfusion catheter.
 29. The method of claim 28, wherein theperfusate flows in the direction of the discharge channel in a lumendefined between the injection needle and the perfusion catheter.
 30. Themethod of claim 29, further comprising absorbing the at least oneconstituent from the body fluid into the perfusate through at least oneopening in the perfusion catheter, wherein the at least one constituentis pulled into the lumen across a concentration gradient created as theperfusate is guided away from the discharge opening in the distal end ofthe injection needle.
 31. The method of claim 30, further comprisingcausing the perfusate and the at least one constituent to flow out ofthe lumen through the discharge channel.
 32. The method of claim 26,further comprising providing a sensor to ascertain information about theat least one constituent, the sensor being placed downstream of theperfusion catheter.
 33. The method of claim 26, further comprisingproviding a working electrode in the discharge channel and providing acounter electrode to the working electrode.
 34. A method of obtaining atleast one constituent of a body fluid, comprising: providing a perfusioncatheter comprising a proximal end in fluid communication with adischarge channel and a distal end including a distal opening; providinga hollow injection needle slideably displaceable in the perfusioncatheter and including a proximal end capable of being placed in fluidcommunication with a perfusate and a distal end including a dischargeopening; extending the distal end of the injection needle through thedistal opening of the perfusion catheter; inserting the perfusioncatheter into a tissue containing the at least one constituent when thedistal end of the injection needle is protruding from the distal end ofthe perfusion catheter; retracting the injection needle until thedischarge opening of the injection needle resides within the perfusioncatheter; and causing perfusate to flow from said discharge opening intothe perfusion catheter.
 35. The method of claim 34, wherein the flowingperfusate causes body fluid to be sucked into the perfusion catheter.36. The method of claim 35, wherein the perfusate flows in the directionof the discharge channel in a lumen defined between the injection needleand the perfusion catheter.
 37. The method of claim 34, furthercomprising absorbing the at least one constituent from the body fluidinto the perfusate through at least one opening in the perfusioncatheter, wherein the at least one constituent is pulled into the lumenacross a concentration gradient created as the perfusate is guided awayfrom the discharge opening in the distal end of the injection needle.38. The method of claim 37, further comprising causing the perfusate andthe at least one constituent to flow out of the lumen through thedischarge channel.
 39. The method of claim 34, further comprisingextending the distal end of the injection needle through the distalopening of the perfusion catheter.
 40. The method of claim 34, furthercomprising providing a sensor to ascertain information about the atleast one constituent, the sensor being placed downstream of theperfusion catheter.
 41. The method of claim 34, further comprisingproviding a working electrode in the discharge channel and providing acounter electrode to the working electrode.